Wafer handling traction control system

ABSTRACT

A wafer handling traction control system is provided that is able to detect slippage of a semiconductor wafer with respect to an end effector and is able to adjust the end effector&#39;s movement in order to minimize further slippage. Upon the detection of relative motion of the semiconductor wafer with respect to the end effector past a threshold amount, the end effector&#39;s movements are adjusted to minimize slippage of the semiconductor wafer. The wafer handling traction control system may include a sensor that detects relative motion between the semiconductor wafer and the end effector.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/166,771, filed on Jan. 28, 2014, and titled “Wafer Handling TractionControl System.”

BACKGROUND

Robot arms with end effectors are used to pick and place semiconductorwafers. The end effectors may typically be a “blade” type end effector,e.g., spatula-like. Many blade-type end effectors rely on gravity andfriction to hold the semiconductor wafer in place and moving the endeffector too quickly may cause the semiconductor wafer to slip off theend effector. One conventional approach is to utilize a sensor orsensors to detect when the semiconductor wafer is no longer on the endeffector, e.g., the wafer has fallen off, and to stop the robot arm whensuch an event has occurred.

SUMMARY

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale unless specifically indicated as being scaled drawings.

In some implementations, an apparatus for use with semiconductorprocessing equipment may be provided. The apparatus may include a firstrobot arm configured to support a first semiconductor wafer on a firstend effector, a first sensor configured to detect relative movementbetween the first semiconductor wafer and the first end effector, and acontroller with one or more processors and a memory. The one or moreprocessors, the memory, the first robotic arm, and the first sensor maybe communicatively connected. The memory may store program instructionsfor controlling the one or more processors to: a) cause the first robotarm to move according to a first acceleration profile while the firstsemiconductor wafer is supported by the first end effector, b) receivefirst sensor data from the first sensor, c) analyze the first sensordata to determine first motion data based on relative movement of thefirst semiconductor wafer with respect to the first end effector duringmotion of the first robot arm while the first semiconductor wafer issupported by the first end effector, d) determine whether the firstmotion data attributable to movement of the first robot arm according tothe first acceleration profile exceeds a first threshold motion metric,and e) cause the first robot arm to move according to a secondacceleration profile when the first motion data attributable to movementof the first robot arm according to the first acceleration profileexceeds the first threshold motion metric. The first motion dataattributable to movement of the first robot arm according to the secondacceleration profile may stay within the first threshold motion metric.

In some such implementations of the apparatus, the first motion data maybe based on data from which the relative acceleration of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector can be calculated. In some suchimplementations, the first threshold motion metric may be relativeacceleration of between about 0.001 and 100 m²/s of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector. In some other or additional suchimplementations, the first threshold motion metric may be relativeacceleration of between about 1 and 10 m²/s of the first semiconductorwafer with respect to the first end effector during motion of the firstrobot arm while the first semiconductor wafer is supported by the firstend effector.

In some other or additional implementations of the apparatus, the firstmotion data may be based on data from which the relative velocity of thefirst semiconductor wafer with respect to the first end effector duringmotion of the first robot arm while the first semiconductor wafer issupported by the first end effector can be calculated. In some suchimplementations, the first threshold motion metric may be a relativevelocity of between about 0.001 and 100 m/s of the first semiconductorwafer with respect to the first end effector during motion of the firstrobot arm while the first semiconductor wafer is supported by the firstend effector. In some other or additional such implementations, thefirst threshold motion metric may be a relative velocity of betweenabout 0.5 and 10 m/s of the first semiconductor wafer with respect tothe first end effector during motion of the first robot arm while thefirst semiconductor wafer is supported by the first end effector.

In some other or additional implementations of the apparatus, the firstmotion data may be based on the relative displacement of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector. In some such implementations, the firstthreshold motion metric may be a relative displacement of between about0.001 and 100 mm of the first semiconductor wafer with respect to thefirst end effector during motion of the first robot arm while the firstsemiconductor wafer is supported by the first end effector. In someother or additional such implementations, the first threshold motionmetric may be a relative displacement of between about 0.5 and 4 mm ofthe first semiconductor wafer with respect to the first end effectorduring motion of the first robot arm while the first semiconductor waferis supported by the first end effector.

In some other or additional implementations of the apparatus, the firstmotion data may be based on a combination of two or more relative motionparameters selected from the group consisting of: relative acceleration(of the first semiconductor wafer with respect to the first end effectorduring motion of the first robot arm while the first semiconductor waferis supported by the first end effector), relative velocity (of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector), and relative displacement of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector.

In some other or additional implementations, the apparatus may furtherinclude a wafer aligner configured to support the first semiconductorwafer and the memory may store further instructions for additionallycontrolling the one or more processors to cause the first robot arm toplace the first semiconductor wafer on the wafer aligner to correct forrelative displacement of the first semiconductor wafer with respect tothe first end effector that occurred during a) and e).

In some other or additional implementations, the apparatus' firstacceleration profile may be a first calibration acceleration profile,the second acceleration profile may be a second calibration accelerationprofile, and the memory may store further instructions for additionallycontrolling the one or more processors to: f) cause the first robot armto move according to a first operational acceleration profile associatedwith the first calibration acceleration profile after d) when the firstmotion data attributable to the movement of the first robot armaccording to the first acceleration profile does not exceed the firstthreshold motion metric, and g) cause the first robot arm to moveaccording to a second operational acceleration profile associated withthe second calibration acceleration profile after e) when the firstmotion data attributable to the movement of the first robot armaccording to the first acceleration profile exceeds the first thresholdmotion metric and the first motion data attributable to the movement ofthe first robot arm according to the second acceleration profile doesnot exceed the first threshold motion metric.

In some other or additional implementations, the apparatus' memory maystore further instructions for additionally controlling the one or moreprocessors to, prior to a) and e): h) determine, after f) or g), whetherthe first motion data attributable to the movement of the first robotarm according to the first or second operational acceleration profileexceeds a second threshold motion metric, i) cause the first robot armto move according to a third operational acceleration profile when thefirst motion data attributable to the movement of the first robot armaccording to the first or second operational acceleration profileexceeds the second threshold motion metric, when the first motion dataattributable to the movement of the first robot arm according to thethird operational acceleration profile stays within the second thresholdmotion metric.

In some such implementations, the memory may store further instructionsfor additionally controlling the one or more processors to: j) cause thefirst robot arm to move N additional times according to the firstoperational acceleration profile after d) and without performing a) ore) for N additional semiconductor wafers when the first motion dataattributable to the movement of the first robot arm according to thefirst calibration acceleration profile does not exceed the firstthreshold motion metric, and k) cause the first robot arm to move Nadditional times according to the second operational accelerationprofile after e) and without performing a) or e) for the N additionalsemiconductor wafers when the first motion data attributable to themovement of the first robot arm according to the first calibrationacceleration profile exceeds the first threshold motion metric and thefirst motion data attributable to the movement of the first robot armaccording to the second calibration acceleration profile does not exceedthe first threshold motion metric, wherein N is an integer greater thanor equal to 1.

In some additional such implementations, the memory may store furtherinstructions for additionally controlling the one or more processors to:l) cause the first robot arm to move according to a third calibrationacceleration profile after d) when the first motion data attributable tomovement of the first robot arm according to the first accelerationprofile is below the first threshold motion metric, when the firstmotion data attributable to movement of the first robot arm according tothe third calibration acceleration profile stays within the firstthreshold motion metric; and m) cause the first robot arm to moveaccording to a third operational acceleration profile associated withthe third calibration acceleration profile after l) when the firstmotion data attributable to the movement of the first robot armaccording to the first acceleration profile is below the first thresholdmotion metric and the first motion data attributable to the movement ofthe first robot arm according to the third acceleration profile does notexceed the first threshold motion metric. In some such implementations,the first motion data attributable to the third calibration accelerationprofile may exceed the first motion data attributable to the firstcalibration acceleration profile.

In some other or additional implementations, the first accelerationprofile of the apparatus may be a first operational accelerationprofile, and the second acceleration profile may be a second operationalacceleration profile.

In some other or additional implementations, the first sensor of theapparatus may be an optical sensor.

In some other or additional implementations, the first sensor of theapparatus may be a vacuum sensor.

In some other or additional implementations, the first robot arm of theapparatus may support the first sensor.

In some other or additional implementations, the first sensor of theapparatus may be supported in a location that is fixed with respect tothe first robot arm.

In some implementations, a semiconductor wafer handling method may beprovided. The method may include: n) moving a first robot arm, includinga first end effector supporting a first semiconductor wafer, accordingto a first calibration acceleration profile, o) receiving first sensordata from a first sensor configured to detect relative movement betweenthe first semiconductor wafer and the first end effector, p) analyzingthe first sensor data to determine first motion data based on relativemovement of the first semiconductor wafer with respect to the first endeffector during motion of the first robot arm while the firstsemiconductor wafer is supported by the first end effector, and q)determining whether the first motion data attributable to movement ofthe first robot arm according to the first calibration accelerationprofile exceeds a first threshold motion metric.

In some such implementations, the method may further include: r)determining that the first motion data attributable to movement of thefirst robot arm according to the first calibration acceleration profileexceeds the first threshold motion metric, s) moving the first robotarm, including the first end effector supporting the first semiconductorwafer, according to a second calibration acceleration profile, t)determining that the first motion data attributable to movement of thefirst robot arm according to the second calibration acceleration profiledoes not exceed the first threshold motion metric, and u) selecting asecond operational acceleration profile associated with the secondcalibration acceleration profile. In some such implementations, themethod may further include: v) moving the first robot arm, after u),according to the second operational acceleration profile associated withthe second calibration acceleration profile.

In some further or additional implementations, the method may furtherinclude: w) determining that the first motion data attributable tomovement of the first robot arm according to the first calibrationacceleration profile does not exceed the first threshold motion metric,and x) selecting a first operational acceleration profile associatedwith the first calibration acceleration profile. In some suchimplementations, the method may further include: y) moving the firstrobot arm, after x), according to the first operational accelerationprofile associated with the first calibration acceleration profile.

In some implementations, another semiconductor wafer handling method maybe provided. The method may include: moving a first robot arm, includinga first end effector supporting a first semiconductor wafer, accordingto a first operational acceleration profile, receiving a first sensordata from a first sensor configured to detect relative movement betweenthe first semiconductor wafer and the first end effector, analyzing thefirst sensor data to determine a first motion data based on relativemovement of the first semiconductor wafer with respect to the first endeffector during motion of the first robot arm while the firstsemiconductor wafer is supported by the first end effector, determiningthat the first motion data attributable to movement of the first robotarm according to the first operational acceleration profile exceeds afirst threshold motion metric, and moving the first robot arm accordingto a second operational acceleration profile when the first motion dataattributable to movement of the first robot arm according to the firstoperational acceleration profile exceeds the first threshold motionmetric, when the first motion data attributable to movement of the firstrobot arm according to the second operational acceleration profile stayswithin the first threshold motion metric.

In some such implementations, the method may further include that thefirst operational acceleration profile is a pre-determined accelerationprofile. In some such implementations, the method's second operationalacceleration profile is a pre-determined acceleration profile.

In some further or additional implementations, the method may furtherinclude moving the first robot arm N additional times according to thesecond operational acceleration profile for N additional semiconductorwafers when the first motion data attributable to the movement of thefirst robot arm according to the first operational acceleration profileexceeds the first threshold motion metric and the first motion dataattributable to the movement of the first robot arm according to thesecond operational acceleration profile does not exceed the firstthreshold motion metric, wherein N is an integer greater than or equalto 1.

These and other aspects of this disclosure are explained in more detailwith reference to the accompanying Figures listed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram representation of certain components of asemiconductor wafer handling system utilizing a wafer handling tractioncontrol system.

FIG. 2 shows a flow diagram detailing an example technique for waferhandling traction control.

FIG. 3 is a graph of the motion of an end effector and a semiconductorwafer supported by the end effector with portions highlighted whererelative motion between the end effector and the semiconductor wafer hasoccurred.

FIG. 4 is a graph of example acceleration profiles for an end effector.

FIG. 5 shows graphs of the acceleration, velocity, and displacement ofan end effector and a semiconductor wafer supported by the end effector.

FIG. 6 is a graph showing wafer slippage versus force applied.

FIG. 7 shows a flow diagram detailing an example technique for slipthreshold detection wafer handling traction control using calibrationacceleration profiles.

FIG. 8 shows a flow diagram detailing an example technique for real-timewafer handling traction control.

FIG. 9 shows a flow diagram detailing an example of a techniquecombining slip threshold detection wafer handling traction control usingcalibration acceleration profiles combined with real-time detectionwafer handling traction control.

FIG. 10A is a graph showing example partial acceleration profiles and anexample of determining a final acceleration profile from an originalacceleration profile.

FIG. 10B is another graph showing example partial acceleration profilesand an example of determining a final acceleration profile from anoriginal acceleration profile.

FIG. 10C is a graph showing example partial acceleration profiles thatmay be used in determining an operational acceleration profile from acalibration acceleration profile.

DETAILED DESCRIPTION

The present inventor has conceived of a wafer handling traction controlsystem that is able to detect slippage of a semiconductor wafer withrespect to an end effector that supports and moves the semiconductorwafer and that is able to adjust the end effector's movement in order tominimize further slippage. The wafer handling traction control systemmay include a sensor that detects relative motion between thesemiconductor wafer and the end effector. Upon the detection of relativemotion past a threshold amount, the end effector's movements areadjusted to reduce or eliminate slippage of the semiconductor wafer.

It is to be understood that, as used herein, the term “semiconductorwafer” may refer both to wafers that are made of a semiconductormaterial, e.g., silicon, and wafers that are made of materials that arenot generally identified as semiconductors, e.g., epoxy, but thattypically have semiconductor materials deposited on them during asemiconductor manufacturing process. Handling of both types of wafers isconsidered to be within the scope of this disclosure.

Robot arms with end effectors are used to pick and place semiconductorwafers. The end effectors are typically configured to support thesemiconductor wafer while the semiconductor wafer moves to adestination, e.g. a semiconductor process chamber, loadlock, or otherstation. One conventional approach to semiconductor wafer handling is toutilize a sensor or sensors to detect when the semiconductor wafer is nolonger supported by the end effector and to stop movement of the robotarm when the semiconductor wafer is no longer supported by the endeffector. In this conventional approach, movement of the robot arm isnot adjusted before the end effector no longer supports thesemiconductor wafer. By contrast, wafer handling traction controlsystems such as described herein are able to detect the slippage past acertain threshold of the semiconductor wafer relative to the endeffector and adjust the movement of the robot arm so that thesemiconductor wafer does not slip off the end effector during furthermovement of the end effector.

FIG. 1 shows a diagram representation of certain components of asemiconductor wafer handling system utilizing a wafer handling tractioncontrol system. The implementation shown in FIG. 1 includes a firstrobot arm 102 with an end effector 112, a semiconductor wafer 104, acontroller 106, a sensor 108, and a motor 110. The components shown inFIG. 1 may be a part of a semiconductor tool.

The robot arm 102 is configured to handle a semiconductor wafer ormultiple semiconductor wafers. The robot arm 102 may be configured tomove from at least a first position to a second position duringsemiconductor wafer handling. In certain implementations, the robot arm102 may be configured to also move between additional positions.

The robot arm 102 may include the end effector 112. The end effector 112may be configured to hold the semiconductor wafer 104 duringsemiconductor wafer handling. The end effector 112 may typically be a“blade” type end effector, e.g., spatula-like. Many blade-type endeffectors rely on gravity and friction to hold the semiconductor waferin place with respect to the end effector during movement; moving theend effector too quickly may cause the inertial forces of thesemiconductor wafer to overcome the friction forces due to gravity—thiscauses the semiconductor wafer to slip with respect to the end effector.It is also common for the semiconductor wafer 104 to be supported by theend effector 112 in a manner that reduces contact between thesemiconductor wafer 104 and the end effector 112 to reduce the risk ofdamage to the semiconductor wafer 104 or the potential for generatingparticulates. One common mechanism for providing such reduced wafer/endeffector contact is to utilize a plurality of contact pads, e.g., threeor four contact pads. The contact pads may be made from a compliantmaterial, e.g., an elastomer, to reduce the risk of damage to thesemiconductor wafer 104 and to increase the static and dynamic frictionconstants that act on the semiconductor wafer/end effector contactinterface. These contact pads may be quite small, e.g., less than 0.25″in diameter in the contact area. Robot arm 102 may be moved by the motor110. The motor 110 may be any type of suitable motor including steppermotors. The motor 110 may directly move the robot arm 102 or may movethe robot arm 102 indirectly through a drive mechanism connected to therobot arm 102. When the robot arm 102 is moved, the end effector 112 maybe moved as well according to the movements of the robot arm 102. Incertain implementations, there may be more than one robot arm, each withits own end effector.

The controller 106 may control the motor 110. The controller 106 mayinclude one or more physical or logical controllers, one or more memorydevices, and one or more processors. The processor may include a centralprocessing unit (CPU) or computer, analog and/or digital input/outputconnections, stepper motor controller boards, and other like components.Instructions for implementing appropriate control operations may beexecuted by the processor. These instructions may be stored on thememory devices associated with or part of the controller or they may beprovided over a network. In certain implementations, the controller 106executes system control software or logic.

The system control logic may include instructions for controlling themotor, controlling the movement of the robot arm through the motor,receiving signals from the sensor, as well as other instructions neededduring semiconductor wafer handling according to the various techniquesdiscussed herein. The system control logic for controlling the motor mayinclude controlling the motor through instructions for the motor to runaccording to various acceleration profiles.

Typically, the acceleration profile (or commands and data that cause themotor(s) to operate according to a particular acceleration profile) willbe stored in the memory of the controller or in a memory accessible bythe controller, e.g., a network storage system. The controller may becoupled to the motor and output command instructions, e.g. voltages, bitsignals, etc., to the motor to control the motor's movement of the robotarm according to a selected acceleration profile. The accelerationprofile may be provided to the motor directly, e.g., the motor mayaccept input in the form of a voltage signal that controls motoracceleration, or the acceleration profile may be provided to the motorindirectly, e.g., the motor may accept input in the form of a voltagesignal that controls motor velocity (and thus the speed with which thevoltage signal changes may result in a particular acceleration).

System control logic may be provided using various types oftechnologies, including, but not limited to, the examples discussedherein. For example, in general, the instructions used to control theapparatus may be designed or configured in hardware and/or software. Itmay be said that the instructions are provided by “programming”. Theprogramming may be hard-coded, e.g., in digital signal processors, aspart of an application-specific integrated circuit (ASIC), or otherdevices which have specific algorithms implemented as hardware. In otherimplementations, programming may be provided as software stored involatile or non-volatile memory. Programming is also understood toinclude software or firmware instructions that may be executed on ageneral purpose processor. System control software may be coded in anysuitable computer-readable programming language.

Various subroutines or control objects may be written to controloperation of the motor and the robot arm for handling semiconductorwafers. In some implementations, system control software may includeinput/output control (IOC) sequencing instructions for controlling thevarious parameters described herein. For example, the semiconductorwafer handling process may be broken into multiple phases withcorrespondingly different acceleration curves or profiles, each of whichmay be defined by its own set of acceleration parameters. Each phase ofa semiconductor wafer handling process may be controlled by one or moreinstructions executed by the system controller.

In some implementations, there may be a user interface associated withthe system controller. The user interface may include a display screen,graphical software displays of the apparatus and/or process conditions,and user input devices such as pointing devices, keyboards, touchscreens, microphones, etc. Such a user interface may be used, forexample, to adjust various parameters that affect system performance,e.g., acceleration curves, setpoints, thresholds, etc.

In some implementations, parameters relating to operation conditions maybe adjusted by the system controller. Non-limiting examples include thesize of the semiconductor wafer, the configuration of the end effectorsupporting the semiconductor wafer, the type of semiconductor waferhandled, etc.

Signals for monitoring the semiconductor wafer handling process may beprovided by analog and/or digital input connections of the systemcontroller with a sensor or multiple sensors. The signals forcontrolling the wafer handling process may be received by the controllervia analog and/or digital output connections of the robot, motor, and/orsensor. Non-limiting examples of sensors (in addition to sensor 108)that may be used to monitor the semiconductor wafer handling processinclude sensors for measuring the angle of rotation of the semiconductorwafer, the position of the semiconductor wafer, the angle of rotation ofthe end effector, the position of the end effector, etc. Appropriatelyprogrammed feedback and control algorithms may be used with data fromthese sensors to maintain process control of the robot arm.

The sensor 108 may be configured to detect the relative motion of thesemiconductor wafer 104 relative to the end effector 112 and outputsensor data indicative of such relative motion to the controller 106.Certain implementations of wafer handling traction control may utilizesensors that may detect the motion of the end effector and/or thesemiconductor wafer relative to a certain frame of reference. The frameof reference may be any frame of reference fixed or moving, including,but not limited to the end effector or another frame of reference. Themotion detected by the sensor may be acceleration, velocity,displacement, or another type of motion. The controller may containlogic to calculate other types of motions from the motion detected. Forexample, if an implementation contains a sensor that detectsdisplacement, the controller may calculate velocity from the detecteddisplacement through measuring the change in displacement compared totiming signals from an internal clock in the controller. The change indisplacement through time would indicate velocity.

In certain implementations, the sensor 108 may be configured to detectrelative motion of the semiconductor wafer 104 with respect to the endeffector 112 through a feature on the semiconductor wafer 104 such as anotch, a slot, a pattern, or another feature that may be readilydetectable by the sensor 108. In other implementations, the sensor 108may be configured to detect relative motion of the semiconductor wafer104 with respect to the end effector 112 without any correspondingengineered feature on the semiconductor wafer 104. Instead, the sensor108 may detect the movement of the semiconductor wafer 104 with respectto the end effector 112 by monitoring the surface of the semiconductorwafer.

The sensor 108 may, for example, be an optical sensor supported on theend effector 112 that emits a beam of light that is configured tointeract with a pattern on the semiconductor wafer 104. Such a patternmay be an engineered pattern, e.g., a photolithographically-producedpattern, or it may be a texture or pattern that is inherent to thesemiconductor wafer 104, e.g., the surface finish or roughness of thesemiconductor wafer may prove to be sufficiently rough that an opticaldetector may be capable of registering the surface roughness andmeasuring the amount of displacement that occurs when the semiconductorwafer 104 slips with respect to the end effector 112, e.g., by theamount that a particular surface roughness pattern “moves.” The amountof light reflected by the pattern may change depending on which area ofthe pattern the light shines on. Relative motion between thesemiconductor wafer 104 and the end effector 112 may be detected by thesensor 108 through changes in the amount of light reflected. The sensor108 may output the sensor data detailing the amount of light reflectedto the controller 106. Through the changes in the amount of lightreflected, the controller may be able to determine first motion data.The first motion data may be indicative of the relative motion of thesemiconductor wafer 104 with respect to the end effector 112. Dependingon the first motion data derived, the controller 106 may elect to changethe acceleration profile according to which the motor 110 runs. In otherimplementations, other sensors may be used as well, including, but notlimited to, machine vision sensors (which may move with the base and therobotic arm, or which may observe the robotic arm from a fixed positionremote from the base and the robotic arm). Other implementations mayalso mount the sensor in other locations, such as through accelerometersmounted on the semiconductor wafer, the accelerometer acting as amounted sensor to detect motion of the semiconductor wafer. Such animplementation may use the semiconductor wafer with the mounted sensoras a calibration wafer. The calibration wafer may be used for slipthreshold detection of a batch of similar semiconductor wafers in amanner similar to that detailed in FIG. 7.

An example of a suitable sensor 108 may be an optical sensor such as isused on an optical mouse. Past optical sensors for computer mice haverequired that the mouse be used on rough or non-shiny surfaces in orderto provide accurate measurement of the movement of the mouse withrespect to the mousing surface. More recent mouse designs, e.g., mousedesigns with photon based sensors such as LED or laser mice, haveincorporated more sensitive optical detectors capable of providingaccurate mouse movement measurements on highly polished surfaces, e.g.,glass. Similar sensors may be used to measure relative motion betweenthe semiconductor wafer and the end effector.

Other types of optical sensors may also be suitable sensors. Forexample, machine imaging sensors or charge coupled devices (“CCD”) maybe used. Such sensors may detect movement through imaging of thesemiconductor wafer from above, or through an array of sensors locatedaround the edges of the semiconductor wafer to detect movement of theedges of the semiconductor wafer (for example, two linear-strip CCDdevices on the end effector and aligned with radii of a wafer and placedsuch that the wafer edge is nominally centered on both strips may serveto provide measurements of edge location at two points on thecircumference of the wafer, allowing the wafer position to becalculated). Broken-beam sensors may also be used to detect movement ofthe edges of the semiconductor wafer. Alternatively, multiple ultrasonicsensors configured to measure the distance to the edge of thesemiconductor wafer may also be used to detect movement of the edges ofthe semiconductor wafer.

Another example of a suitable sensor 108 may be a mechanical sensor,such as a small rotating sensor, e.g., a scroll wheel or ball, touchingthe bottom of the semiconductor wafer.

FIG. 2 shows a flow diagram detailing an example technique for waferhandling traction control. FIG. 2 shows the operation of semiconductorwafer handling utilizing a wafer handling traction control system at ahigh level. FIG. 2 may be performed in a test procedure before thesemiconductor wafer has been transported to its destination, or FIG. 2may be performed as the semiconductor wafer is being transported to itsdestination—the first/second acceleration profiles indicated may becalibration acceleration profiles or operational acceleration profiles,depending on the particular wafer traction control technique utilized.Some techniques, discussed later in this paper, may utilize both typesof profiles.

In block 202 the controller may instruct the motor to move the endeffector according to a first acceleration profile. In block 202, theend effector is moved while the end effector is supporting thesemiconductor wafer.

While the end effector is moved according to the first accelerationprofile, any relative motion of the semiconductor wafer with respect tothe end effector may be monitored, as shown in block 204. In certainimplementations, block 204 may monitor the relative motion of thesemiconductor wafer with respect to the end effector through a sensorsupported by the end effector, another portion of the robot arm, ormounted to another portion of the semiconductor tool; the sensor mayproduce relative motion data that is indicative of the relative motion,if any, between the semiconductor wafer and the end effector.

In block 206, the relative motion data may be analyzed by the controllerand used to derive a first motion data. For example, the first motiondata may be based on the relative displacement, relative velocity,relative acceleration, or relative jerk of the semiconductor wafer withrespect to the end effector, as derivable from the relative motion data.In some cases, the first motion data may be the same as the relativemotion data. For example, if the first motion data is displacement andthe sensor used outputs relative motion data that indicatesdisplacement, then the analysis that is performed may consist, in someexamples, of merely treating the relative motion data as the firstmotion data. In other cases, there may be more involved processingneeded. For example, displacement-type relative motion data may betransformed into velocity-type or acceleration-type first motion data byperforming one or more differentiations. In some cases, it may benecessary to apply various correction factors or scaling factors to therelative motion data produced by the sensor to obtain first motion datathat is calibrated to established unit systems, e.g., the relativemotion data may be in the form of volts, and a conversion factor may beused to transform such voltage output into displacement units, e.g., Xmillimeters per millivolt. The first motion data may also be derivedfrom inputting relative motion data into an equation, e.g., the firstmotion data may be the output of an equation utilizing the relativevelocity and relative acceleration as inputs. An equation of such anequation would be 2v+4a where “v” is the relative velocity and “a” isthe relative acceleration. In the example equation, relativeacceleration is weighted twice as much as relative velocity. In othersuch equations, the weighting given to different types of relativemotion data may be unequal, e.g., relative velocity may be weightedhigher than relative acceleration or relative displacement, or theweighting of a type of relative motion may change depending on themagnitude of that type of relative motion, e.g., relative velocity above2 m/s may be given twice the weight as relative velocity equal to orbelow 2 m/s.

If the first motion data exceeds a certain threshold, such as a firstthreshold motion metric, the controller instructs the motor to move theend effector according to a second acceleration profile, as shown inblock 208. The first threshold motion metric may, for example, be amaximum total amount of relative displacement that occurs duringmovement according to the first acceleration profile, a maximum relativevelocity between the semiconductor wafer and the end effector, or othermetric that may be determined to indicate unacceptable relative slipbetween the semiconductor wafer and the end effector. In certainimplementations, movement of the end effector according to the secondacceleration profile is configured to result in lower first motion datathan movement of the end effector according to the first accelerationprofile. The second acceleration profile may be an acceleration profilewhich accelerates or decelerates the end effector at a lower rate thanthe first acceleration profile in certain portions of the accelerationprofile or throughout the entire acceleration profile.

FIG. 3 is a graph of the motion of an end effector and a semiconductorwafer supported by the end effector with portions highlighted whererelative motion between the end effector and the semiconductor wafer hasoccurred. In FIG. 3, the solid line is the plot of the motion for theend effector while the dotted line is the plot of the motion for thesemiconductor wafer. The motion of the end effector and thesemiconductor wafer in FIG. 3 should not be confused with the firstmotion data of block 206. The first motion data may be derived from therelative motion of the semiconductor wafer with respect to the endeffector while the graph in FIG. 3 shows the individual absolute motionsof the end effector and the semiconductor wafer with respect to a commonreference frame, though the relative motion between the end effector andthe semiconductor wafer may be calculated by comparing the two datasets. The motion in FIG. 3 may be any type of motion includingdisplacement, velocity, and acceleration.

The y-axis of FIG. 3 corresponds to the magnitude of the motion. In FIG.3, the y-axis is shown in a linear scale. The x-axis of FIG. 3corresponds to time.

Sections 302 and 304 in FIG. 3 are two sections of the graph of themotion of the end effector and the semiconductor wafer that showrelative motion between the end effector and the semiconductor waferwhich may exceed the certain threshold. Several methods may be used todetermine that the relative motion between the end effector and thesemiconductor wafer has exceeded the threshold. These methods includecomparing the difference in magnitude between the end effector motionplot and the semiconductor wafer motion plot at certain points in timein sections 302 and 304 to a threshold magnitude to determine whether aninstantaneous relative motion threshold of the semiconductor wafer withrespect to the end effector has been exceeded, comparing the differencein area under the curve of the plots of the end effector motion and thesemiconductor wafer motion (shown as the gray areas in FIG. 3) to athreshold area to determine whether a total relative motion threshold ofthe semiconductor wafer with respect to the end effector has beenexceeded, as well as other methods.

In FIG. 3, section 306 shows a section where the relative motion betweenthe end effector and the semiconductor wafer may not have exceeded thethreshold even though there is a difference between the motion of theend effector and the motion of the semiconductor wafer. In section 306,the relative motion between the end effector and the semiconductor wafermay be determined to have not exceeded the threshold by comparing thedifference in magnitude between the end effector motion plot and thesemiconductor wafer motion plot at any point in time in section 306 todetermine that an instantaneous relative motion threshold of thesemiconductor wafer with respect to the end effector has not beenexceeded, by comparing the difference in area under the curve of theplots of the end effector motion and the semiconductor wafer motion todetermine that a total relative motion threshold of the semiconductorwafer with respect to the end effector has not been exceeded, as well asother methods.

FIG. 4 is a graph of example acceleration profiles for an end effector.FIG. 4 shows three example acceleration profiles, a first accelerationprofile, a second acceleration profile, and a third accelerationprofile, plotted against time. The acceleration profiles of FIG. 4 areintended to be demonstrative and not representative. The units shown areintended for reference purposes only. The acceleration profiles shown inFIG. 4 feature linear acceleration, but the acceleration profiles usedmay also include acceleration profiles that include non-linearacceleration. It is to be understood that the use of the term“acceleration” herein encompasses both positive acceleration andnegative acceleration (deceleration).

In FIG. 4, the first acceleration profile is the acceleration profilewith the highest peak acceleration, at a peak acceleration of 0.6nominal acceleration units. The first acceleration profile also has thehighest peak deceleration, at a peak deceleration of −0.6 nominalacceleration units. In FIG. 4, the first acceleration profile has theshortest time spent accelerating and decelerating, at a totalacceleration and deceleration time of 3 nominal time units, since agiven distance may be covered in a shorter time period with higheracceleration and deceleration. In semiconductor wafer handling utilizinga wafer handling traction control system, if relative motion of thesemiconductor wafer with respect to the end effector exceeding thethreshold is detected while accelerating the end effector with the firstacceleration profile, (i.e., if the first motion data exceeds the firstthreshold motion metric) another acceleration profile such as the secondacceleration profile or the third acceleration profile may be selectedand the end effector may be moved according to the newly-selectedacceleration profile.

The second acceleration profile has a peak acceleration of 0.4 nominalacceleration units and a peak deceleration of −0.4 nominal accelerationunits. In FIG. 4, the second acceleration profile has lower peakacceleration/deceleration compared to the peak acceleration/decelerationof the first acceleration profile, but higher peakacceleration/deceleration compared to the peak acceleration/decelerationof the third acceleration profile. In FIG. 4, the second accelerationprofile, at 5 nominal units spent accelerating/decelerating, has alonger time spent accelerating/decelerating compared to the firstacceleration profile and a shorter time spent accelerating/deceleratingcompared to the third acceleration profile. In semiconductor waferhandling utilizing a wafer handling traction control system, if relativemotion of the semiconductor wafer with respect to the end effectorexceeding the threshold is detected while accelerating the end effectorwith the second acceleration profile, another acceleration profile suchas the third acceleration profile may be selected and the end effectormay be moved according to the third acceleration profile.

The third acceleration profile has a peak acceleration of 0.2 nominalacceleration units and a peak deceleration of −0.2 nominal accelerationunits. In FIG. 4, the third acceleration profile is the accelerationprofile with lowest peak acceleration/deceleration and the longest timespent accelerating decelerating at 8 nominal time units.

Other acceleration profiles utilized in semiconductor wafer handlingutilizing wafer handling traction control system may have differentacceleration profile shapes. For example, other acceleration profilesmay accelerate and decelerate multiple times in one profile. For thoseacceleration profiles that accelerate and decelerate multiple times inone profile, each sequence of acceleration or deceleration may havedifferent magnitudes for peak acceleration/deceleration or each sequencemay have the same magnitude for peak acceleration/deceleration. Eachsequence of acceleration or deceleration may also use different amountsof time to reach peak acceleration/deceleration, or each sequence mayuse the same amount of time to reach peak acceleration/deceleration.

When the first motion data attributable to the movement of the firstrobot arm according to a first acceleration profile exceeds the firstthreshold motion metric, the controller may be configured to select thenext acceleration profile that exerts a lower force on the semiconductorwafer.

For example, in FIG. 4, the first acceleration profile may be defined asthe acceleration profile that exerts the most force on the semiconductorwafer; the third acceleration profile may be defined as the accelerationprofile that exerts the least force on the semiconductor wafer; and thesecond acceleration profile may be defined as the acceleration profilethat exerts the second most force on the semiconductor. The controllermay then instruct the motor to move the robot arm according to the firstacceleration profile. If the first motion data of the movement of therobot arm according to the first acceleration profile is determined toexceed the first threshold motion metric, the controller may then selectthe second acceleration profile and instruct the motor to move the robotarm according to the second acceleration profile. If the first motiondata of the movement of the robot arm according to the secondacceleration profile is determined to exceed the first threshold motionmetric, the controller may then select the third acceleration profileand instruct the motor to move the robot arm according to the thirdacceleration profile. In this way, the controller may step through theacceleration profiles so as to expose the semiconductor wafer togradually decreasing forces. Thus, the controller is able to determinethe acceleration profile that may exert the highest forces on thesemiconductor wafer without producing unsatisfactory degrees of relativeslip between the semiconductor wafer and the end effector.

In certain implementations, the controller may be configured to derivesecond motion data and/or utilize a second threshold motion metric ifthe first motion data attributable to movement of the robot armaccording to the first acceleration profile exceeds the first thresholdmotion metric. If the first motion data exceeds the first thresholdmotion metric, the semiconductor wafer may already have displacedrelative to the end effector and so is more likely to slip off the endeffector than when the semiconductor wafer was first picked by the endeffector. The second motion data and/or the second threshold motionmetric may be configured to allow for less relative motion of thesemiconductor wafer with respect to the end effector before thecontroller selects another acceleration profile. Utilization of thesecond motion data and/or second threshold motion metric may allow thecontroller to avoid a situation where, if the first threshold motionmetric is exceeded multiple times, the semiconductor wafer may slip offthe end effector.

In certain implementations, the controller may be programmed to skipacceleration profiles depending on the magnitude of how much the firstmotion data exceeds the first threshold motion metric. For example, ifthe first motion data of the movement of the robot arm according to thefirst acceleration profile exceeds the first threshold motion metric bya sufficient magnitude, the controller may select the third accelerationprofile instead of the second acceleration profile and instruct themotor to move the first robot arm according to the third accelerationprofile. In this case, the controller has skipped the secondacceleration profile.

FIG. 5 shows graphs of the acceleration, velocity, and displacement ofan end effector and a semiconductor wafer supported by the end effector.The graphs show the motion of the end effector and the semiconductorwafer during an example wafer handling sequence. The magnitudes statedfor acceleration, velocity, displacement, and time do not have unitssince the magnitudes are demonstrative.

The left side of FIG. 5 has graphs for the accelerations, velocities,and displacements of the end effector and the semiconductor wafer withrespect to an external frame of reference. In the graphs, the endeffector is represented by the solid gray line while the semiconductorwafer is represented by the dotted black line.

The top left graph of the accelerations of the end effector and thesemiconductor wafer shows an example sequence where the end effectorsupporting the semiconductor wafer is first accelerated and thendecelerated. The velocities corresponding to the accelerations are shownin the middle left graph. The corresponding displacements are shown inthe bottom left graph.

The right side of FIG. 5 has graphs for the relative acceleration,relative velocity, and relative displacement of the semiconductor waferwith respect to the end effector. The relative acceleration, relativevelocity, and relative displacement correspond to the differences inacceleration, velocity, and displacement between the end effector andthe semiconductor wafer in the graphs to the left side of FIG. 5.

The top right graph of the relative acceleration of the semiconductorwafer with respect to the end effector shows the difference between theend effector acceleration and the semiconductor wafer acceleration ofthe top left graph.

The middle right graph is of the relative velocity of the semiconductorwafer with respect to the end effector. The relative velocitycorresponds to the difference in end effector velocity and semiconductorwafer velocity of the middle left graph.

The bottom right graph is of the relative displacement of thesemiconductor wafer with respect to the end effector. The relativedisplacement corresponds to the difference in end effector displacementand semiconductor wafer displacement of the bottom left graph. Incertain implementations, the relative displacement of the semiconductorwafer with respect to the end effector may be detected directly throughthe sensor. For example, an optical sensor (similar to an optical sensorin an optical mouse) may be installed on the end effector, i.e., bestationary with respect to the end effector. The sensor may be orientedsuch that the sensor illuminates a portion of a semiconductor wafer whenthe semiconductor wafer is supported by the end effector. The sensor maythen measure the degree to which the portion of the semiconductor waferthat is illuminated shifts over time, thus providing a directmeasurement of relative displacement between the semiconductor wafer andthe end effector.

In certain implementations, the sensor may detect one, some, or all ofthe acceleration, velocity, and/or displacement of the semiconductorwafer with respect to the end effector. Certain implementations of waferhandling traction control may utilize sensors which may detect themotion of the end effector and/or the semiconductor wafer relative to acertain frame of reference. The frame of reference may be the endeffector, the semiconductor wafer, or another fixed frame of reference.The motion detected by the sensor may be acceleration, velocity,displacement. The controller may contain logic to transform the motiondetected into other types of motion data. For example, if animplementation contains a sensor which detects relative displacement,the controller may calculate relative velocity from the detectedrelative displacement through measuring the change in relativedisplacement compared to an internal clock, indicating time, in thecontroller. The change in relative displacement over time would indicatethe change in relative velocity.

The controller may utilize relative acceleration, relative velocity,and/or relative displacement, as factors in the calculation of the firstmotion data to detect relative motion of the semiconductor wafer withrespect to the end effector past a first threshold motion metric.Relative displacement, relative velocity, or relative acceleration maybe useful for indicating relative motion in different circumstances. Thefirst threshold motion metric may be different in magnitude depending onthe composition of the first motion data. For example, a controllersolely utilizing relative acceleration to derive the first motion datamay have a first threshold motion metric different in magnitude from themagnitude of the first threshold motion metric of a controller solelyutilizing relative velocity to derive the first motion data.

For example, in FIG. 5 at time unit 1, there are approximately 0.5nominal units of relative acceleration, but almost no relative velocityor relative displacement. The magnitude of relative acceleration is muchhigher than the magnitude of relative velocity or displacement. Thus, attime unit 1, a controller configured to solely utilize relativeacceleration to derive a first motion data may detect relative motion ofthe semiconductor wafer with respect to the end effector, (i.e., thefirst motion data exceeds the first threshold motion metric,) but acontroller configured to solely utilize relative velocity or relativedisplacement may not detect relative motion of the semiconductor waferwith respect to the end effector (since, if the controller wereutilizing relative velocity or relative displacement, the first motiondata may not have exceeded the first threshold motion metric due to thelow magnitude of relative velocity or relative displacement).

In another example, a controller configured to derive the first motiondata solely through relative displacement, with a first threshold motionmetric of 1.0 units of relative displacement, may not have the firstmotion data exceed the first threshold motion metric until approximately6 time units. However, a controller configured to derive the firstmotion data solely through relative velocity, with a first thresholdmotion metric of 0.5 units of relative velocity, may have the firstmotion data pass the first threshold motion metric before 4 time units.Since exceeding the first threshold motion metric may cause thecontroller to select a second acceleration profile, in the exampleabove, the second controller calculating the first motion data solelythrough relative velocity will have selected the second accelerationprofile before the first controller calculating the first motion datasolely through relative displacement will have selected the secondacceleration profile.

FIG. 6 is a graph showing wafer slippage versus force applied. FIG. 6 isfor demonstrative purposes only and so all units in FIG. 6 are nominalunits. In FIG. 6, the implementation has a first threshold motion metricof 5 nominal distance units. In FIG. 6, the first motion datacorresponds to the relative displacement of the semiconductor wafer withrespect to the end effector in a linear manner. That is, one nominalunit of the first motion data in FIG. 6 may correspond to one nominalunit of relative displacement of the semiconductor wafer with respect tothe end effector. Other implementations may derive the first motion datausing other factors or combination of factors. For example, otherimplementations may vary the weight of the factors depending on themagnitude of the factors. Thus, for a first motion data derived solelyfrom relative velocity, relative velocity from 0 to 5 m/s may beweighted x (thus, relative velocity of 4 m/s would give a first motiondata with the magnitude of 4), but relative velocity higher than 5 m/smay be weighted 2× (thus relative velocity 6 m/s would give a firstmotion data with the magnitude of 12). Different implementations mayhave their own weighting scale.

In FIG. 6, the relative displacement of the semiconductor wafer versusforce applied is not linear. The semiconductor wafer in FIG. 6 isdisplaced minimally (or not at all) until point 604. At point 604, whichis around 6.8 units of nominal force, the wafer begins to exhibitreadily discernible displacement; this may generally correspond to thepoint where the force acting on the semiconductor wafer has exceeded thestatic friction force of between the semiconductor wafer and the endeffector. After 6.8 units of force, the semiconductor wafer's relativedisplacement increases at a non-linear rate per unit of nominal forceapplied, with increasingly large amounts of displacement per higher unitforce applied. At point 606, which is around 8.6 units of nominal force,the semiconductor wafer has slipped the maximum acceptable amount inthis example. Thus, 602 in FIG. 6 is the part of the graph where thesemiconductor wafer slippage is within the acceptable amount ofsemiconductor wafer slippage.

In certain other implementations, the controller of the wafer handlingtraction control system may be configured to minimize semiconductorwafer slippage by attempting to keep the force applied below 6.8 unitsof force, the point where the semiconductor wafer begins to exhibitreadily discernible displacement.

FIG. 7 shows a flow diagram detailing an example technique for slipthreshold detection wafer handling traction control using calibrationacceleration profiles.

The technique may begin in block 702, where the semiconductor wafer maybe picked by the end effector such that the semiconductor wafer restson, and is supported by, the end effector, e.g., the semiconductor maybe supported on elastomeric pads on the end effector. The end effectormay be attached to a robot arm as detailed in FIG. 1.

In block 703, a calibration acceleration profile is selected.Calibration acceleration profiles, as used herein, are accelerationprofiles that are not used during normal wafer transport from station tostation, but that are instead used by the controller in order todetermine what operational acceleration profile to use during suchnormal wafer transport from station to station. Operational accelerationprofiles, as used herein, are used during wafer transport from stationto station, e.g., they may govern the acceleration of the end effectorsduring normal operational use. Each calibration acceleration profile maycorrespond with an operational acceleration profile. Typically, as shownin FIG. 10C (discussed later), the calibration acceleration profiles mayhave a larger peak magnitude than their corresponding operationalacceleration profiles and may also be much shorter in duration (as theirprimary purpose is to establish the highest acceleration, from a rangeof potential accelerations that does not produce unacceptable levels ofrelative slip between the semiconductor wafer and the end effector).Moving the robot arm with the motor according to the operationalacceleration profile may exert a peak force on the semiconductor waferlower than or equal to the peak force exerted on the semiconductor waferwhile moving the robot arm with the motor according to the correspondingcalibration acceleration profile. Calibration acceleration profiles andoperational acceleration profiles may be profiles pre-loaded into thememory of the controller, determined by the controller during thehandling of semiconductor wafers, input by an operator, or providedthrough other methods such as over a network in communication with thecontroller.

In block 704, the robot arm and the end effector are moved by the motoraccording to the calibration acceleration profile.

In block 706, a determination may be made as to whether there is slip ofthe semiconductor wafer past a threshold amount. In block 706, thesensor may monitor the relative motion of the semiconductor wafer withrespect to the end effector. The sensor may output relative motion datato the controller. Slip may be detected by the controller if the firstmotion data derived from the relative motion data exceeds a firstthreshold motion metric. The first motion data may be derived through avariety of different methods, such as those discussed above with respectto FIG. 5. While the robot arm is moved, the controller may compare thefirst motion data with the first threshold motion metric. If the firstmotion data exceeds the first threshold motion metric, the controllermay determine that there is slip of the semiconductor wafer past thethreshold amount.

If, in block 706, there is slip detected of the semiconductor wafer pastthe threshold amount, a new calibration acceleration profile may beselected, as detailed in block 708. The controller may select a newcalibration acceleration profile that may exert a lower peak force onthe semiconductor wafer, such as through a lower peak acceleration, thanthe calibration acceleration profile that produced slip of thesemiconductor wafer past the threshold amount. The technique may thenreturn to block 704, where the robot arm may be moved according to thenewly-selected calibration acceleration profile.

If no slip of the semiconductor wafer past the threshold amount isdetected in block 706, then the operational acceleration profilecorresponding to the acceleration profile of block 704 may be selectedin block 710.

In block 712, the robot arm and the end effector are moved to thedestination according to the operational acceleration profile selectedin block 710. After the end effector reaches the destination, the endeffector may place the semiconductor wafer in block 714.

In block 716, the end effector may pick, move, and place N additionalsemiconductor wafers according to the selected operational accelerationprofile. After N additional semiconductor wafers are picked, moved, andplaced, FIG. 7 may be repeated starting at block 702.

Thus, FIG. 7 provides a technique that may establish which calibrationacceleration profile of a plurality of calibration acceleration profilesproduces relative slip between a semiconductor wafer and an end effectorthat supports the semiconductor wafer that is below a desired thresholdwhen the end effector is moved by a motor according to the calibrationacceleration profile. In this technique, once a calibration accelerationprofile is determined to produce relative slip that is below the desiredthreshold, then an operational acceleration profile associated with thatcalibration acceleration profile may be selected and the end effectormay be moved by the motor according to that operational accelerationprofile for one or more semiconductor wafers. Thus, a single calibrationoperation, e.g., blocks 703 through 706/708, may be used to select anoperational acceleration profile that may be used for transportingmultiple semiconductor wafers. The number of semiconductor wafers thatmay be transported according to this operational acceleration profilemay, for example, be selected based on a number of factors. For example,one factor may be the total number of wafers transported since the mostrecent calibration operation, e.g., the technique may involverecalibrating every 100 wafers moved. In another example, a group ofsemiconductor wafers may all be made of the same material and have beenexposed to the same processing—such semiconductor wafers may thus bepresumed to have similar material and surface properties and thus likelyhave similar propensities for slip. In such an example, a newcalibration may be performed each time a new batch of semiconductorwafers is transported using the end effector (assuming each batch iscomposed of similar wafers). The technique may thus be thought of as aclosed-loop technique with respect to selecting the operationalacceleration profile and as an open-loop technique with respect toactual wafer transport. Other techniques are discussed further below.

FIG. 8 shows a flow diagram detailing an example technique for real-timewafer handling traction control.

The technique may begin in block 802, where the semiconductor wafer maybe picked by the end effector such that the semiconductor wafer restson, and is supported by, the end effector as detailed in block 702.

In block 803, an operational acceleration profile is selected.

In block 804, the motor moves the robot arm, with the end effectorsupporting the semiconductor wafer, towards a destination according tothe operational acceleration profile.

In block 806, a determination may be made as to whether there is slip ofthe semiconductor wafer past a threshold amount. In block 806, thesensor may monitor the relative motion of the semiconductor wafer withrespect to the end effector similar and output relative motion data tothe controller similar to block 706. Slip may be detected if the firstmotion data derived from the relative motion data exceeds a firstthreshold motion metric.

If, in block 806, there is detected slip of the semiconductor wafer pastthe threshold amount, a new operational acceleration profile may beselected. The controller may select a new operational accelerationprofile that may exert a lower peak force on the semiconductor wafer,such as through a lower peak acceleration, than the operationalacceleration profile that produced slip of the semiconductor wafer pastthe threshold amount. The technique may then return to block 804, wherethe robot arm may be moved according to the newly-selected operationalacceleration profile.

If no slip of the semiconductor wafer past the threshold amount isdetected in block 806, then the robot arm with the end effector may bemoved to the destination by the motor in block 810 according to theoperational acceleration profile selected in block 804. After the endeffector reaches the destination, the end effector may place thesemiconductor wafer in the destination, in a manner similar to how theend effector places the semiconductor wafer in block 712. In certainimplementations, the orientation and or positioning of the semiconductorwafer may be adjusted after the semiconductor wafer has been placed inthe destination. The orientation of the semiconductor wafer may bedetected through the sensor 108 or through other sensors mounted in thesemiconductor tool. The orientation or positioning of the semiconductorwafer may be adjusted by pre-aligners or automatic wafer centering(“AWC”) dynamic aligners with the aid of the sensors.

Thus, FIG. 8 provides a technique where the controller may determine anew operational profile during the transport of semiconductor wafers ifrelative slip above the desired threshold is detected when transportingthe semiconductor wafers according to a previously determinedoperational acceleration profile. The technique may thus be thought ofas an open-loop technique with respect to selecting the initialoperational acceleration profile and a closed-loop technique withrespect to transporting the actual semiconductor wafer. Other techniquesare discussed further below.

FIG. 9 shows a flow diagram detailing an example of a techniquecombining slip threshold detection wafer handling traction control usingcalibration acceleration profiles combined with real-time detectionwafer handling traction control. The semiconductor wafer handlingutilizing a wafer handling traction control detailed in FIG. 9 is acombination of the semiconductor wafer handling techniques detailed inFIG. 7 and FIG. 8.

The technique may begin in block 902, where the semiconductor wafer maybe picked by the end effector in a similar manner to that described inblock 702.

In block 903, a calibration acceleration profile is selected. Thecalibration acceleration profiles and operational acceleration profilesdescribed in FIG. 9 are similar in manner to the calibrationacceleration profiles and operational acceleration profiles describedwith reference to FIGS. 7 and 8.

In block 904, the robot arm and the end effector are moved by the motoraccording to the calibration acceleration profile.

In block 906, a determination may be made as to whether there is slip ofthe semiconductor wafer past a threshold amount. In block 906, thesensor may monitor the relative motion of the semiconductor wafer withrespect to the end effector and output the relative motion data to thecontroller. Slip may be detected by the controller similar to block 706.

If, in block 906, there is slip detected of the semiconductor wafer pastthe threshold amount, a new calibration acceleration profile may beselected, as detailed in block 908. The controller may select a newcalibration acceleration profile in the same manner as that detailed inblock 708. The technique may then return to block 904, where the robotarm may be moved according to the newly-selected calibrationacceleration profile.

If no slip of the semiconductor wafer past the threshold amount isdetected in block 906, then the operational acceleration profilecorresponding to the calibration acceleration profile may be selected inblock 910.

In block 912, the motor moves the robot arm with the end effectorsupporting the semiconductor wafer towards the destination according tothe operational acceleration profile selected in block 710.

In block 914, a determination may be made as to whether there is slip ofthe semiconductor wafer past a threshold amount. In block 914, thesensor may monitor the relative motion of the semiconductor wafer withrespect to the end effector and output the relative motion data to thecontroller similar to block 806. Slip may be detected by the controllersimilar to block 806.

If, in block 914, there is detected slip of the semiconductor wafer pastthe threshold amount, a new operational acceleration profile may beselected. The controller may select a new operational accelerationprofile that may exert a lower peak force on the semiconductor wafer,such as through a lower peak acceleration, than the operationalacceleration profile that produced slip of the semiconductor wafer pastthe threshold amount. The technique may then return to block 912, wherethe robot arm may be moved according to the newly-selected operationalacceleration profile.

If no slip of the semiconductor wafer past the threshold amount isdetected in block 914, then the robot arm with the end effector may bemoved by the motor to the destination in block 918 according to theoperational acceleration profile selected. After the end effectorreaches the destination, the end effector may place the semiconductorwafer in the destination, in a manner similar to how the end effectorplaces the semiconductor wafer in block 712. In certain implementations,the orientation and or positioning of the semiconductor wafer may beadjusted after the semiconductor wafer has been placed in thedestination as in block 712.

Thus, FIG. 9 provides a technique that may establish which calibrationacceleration profile of a plurality of calibration acceleration profilesproduces relative slip between a semiconductor wafer and an end effectorthat supports the semiconductor wafer that is below a desired thresholdwhen the end effector is moved by a motor according to the calibrationacceleration profile. FIG. 9 also provides a technique that maydetermine a new operational acceleration profile if relative slip abovethe desired threshold is detected when transporting the semiconductorwafer according to the previously determined operational accelerationprofile. In this technique, each semiconductor wafer transported has acalibration acceleration profile and an operational acceleration profiledetermined. The technique may thus be thought of as a closed-looptechnique with respect to selecting the operational acceleration profileand transporting the actual semiconductor wafer. In someimplementations, blocks 903 through 910 may be performed for a subset ofwafers in a common batch of wafers, e.g., the first wafer in the batch,and the operational profile that is selected in block 910 for that firstwafer may also be used for the remaining wafers in the batch withoutrepeating blocks 903 through 910 for the remaining wafers in the batch.

FIG. 10A is a graph showing example partial acceleration profiles and anexample of determining a final acceleration profile from an originalacceleration profile. FIG. 10A shows five different example partialacceleration profiles. In the implementation in FIG. 10A, the exampleacceleration profiles are previously programmed into the memory of thecontroller. The example partial acceleration profiles in FIG. 10A areexample partial operational acceleration profiles. A technique similarto the technique detailed in FIG. 10A may be applied to calibrationacceleration profiles to determine the final calibration accelerationprofile.

In FIG. 10A, the controller first selects the original accelerationprofile. The original acceleration profile in FIG. 10A is the firstacceleration profile. The controller instructs the motor to move therobot arm according to the first acceleration profile. In FIG. 10A,while the robot arm is moved, the sensor may monitor the relative motionof the semiconductor wafer with respect to the end effector and outputthe sensor data to the controller in a manner similar to the mannerdescribed in FIG. 1. The controller may derive a first motion data fromthe relative motion data and determine whether the first motion dataexceeds the first threshold motion metric.

In FIG. 10A, the controller determines at point 1002 that the firstmotion data of the movement of the robot arm according to the firstacceleration profile exceeds the first threshold motion metric. Thecontroller then selects the second acceleration profile and instructsthe motor to move the robot arm according to the second accelerationprofile. The second acceleration profile has a lower maximumacceleration than the first acceleration profile. Movement of the robotarm according to the second acceleration profile is configured to resultin a lower peak force exerted on the semiconductor wafer than movementof the robot arm according to the first acceleration profile.

After the second acceleration profile is selected, the controller inFIG. 10A then determines at point 1004 that the first motion data ofmovement of the robot arm according to the second acceleration profileexceeds the first threshold motion metric. The controller then selectsthe third acceleration profile and instructs the motor to move the robotarm according to the third acceleration profile. In FIG. 10A, the thirdacceleration profile has the lowest maximum acceleration. Movement ofthe robot arm according to the third acceleration profile is configuredto result in the lowest peak force exerted on the semiconductor of anyacceleration profile in FIG. 10A. In FIG. 10A, movement of the robot armaccording to the third acceleration profile results in a first motiondata lower than the first threshold motion metric. Thus, the controllercontinues instructing the motor to move the robot arm according to thethird acceleration profile until the end effector reaches thedestination.

In certain implementations, if movement of the robot arm according tothe lowest available acceleration profile results in a first motion dataexceeding the first threshold motion metric, then the controller isconfigured to halt movement of the robot arm. In FIG. 10A, the lowestavailable acceleration profile is the third acceleration profile.

FIG. 10A has two unused additional acceleration profiles. Movement ofthe robot arm according to any of the two additional accelerationprofiles is configured to result in a higher peak force exerted on thesemiconductor wafer than movement of the robot arm according to thefirst acceleration profile. In certain implementations, the controllermay be configured to select one of the two additional accelerationprofiles as the original acceleration profile, e.g., the controller maystart with the acceleration profile that has the highest peakaccelerations and then progress downwards through the availableacceleration profiles as needed in response to detected slip.

FIG. 10B is another graph showing example partial acceleration profilesand an example of determining a final acceleration profile from anoriginal acceleration profile. FIG. 10B shows five different examplepartial acceleration profiles. In the implementation in FIG. 10B, theexample acceleration profiles are previously programmed into the memoryof the controller. The example partial acceleration profiles in FIG. 10Bare example partial operational acceleration profiles. A techniquesimilar to the technique detailed in FIG. 10B may be applied tocalibration acceleration profiles to determine the final calibrationacceleration profile.

In FIG. 10B, the controller first selects the original accelerationprofile. The original acceleration profile in FIG. 10A is the firstacceleration profile and is similar to the first acceleration profile inFIG. 10A. The controller instructs the motor to move the robot armaccording to the first acceleration profile. While the robot arm ismoved, the sensor may monitor the relative motion of the semiconductorwafer with respect to the end effector in a manner and output therelative motion data similar to FIG. 10A. The controller may derive afirst motion data from the relative motion data and determine whetherthe first motion data exceeds the first threshold motion metric.

In FIG. 10B, the controller determines at point 1006 that the firstmotion data of movement of the robot arm according to the firstacceleration profile is lower than the first threshold motion metric.The controller then selects the second acceleration profile andinstructs the motor to move the robot arm according to the secondacceleration profile. The second acceleration profile has a highermaximum acceleration than the first acceleration profile. Movement ofthe robot arm according to the second acceleration profile is configuredto result in a higher peak force exerted on the semiconductor wafer thanmovement of the robot arm according to the first acceleration profile.

After the second acceleration profile is selected, the controller inFIG. 10B then determines at point 1008 that the first motion data ofmovement of the robot arm according to the second acceleration profileis lower than the first threshold motion metric. The controller thenselects the third acceleration profile and instructs the motor to movethe robot arm according to the third acceleration profile. The thirdacceleration profile has the highest maximum acceleration. Movement ofthe robot arm according to the third acceleration profile is configuredto result in the highest peak force exerted on the semiconductor waferof any acceleration profile in FIG. 10B.

After the third acceleration profile is selected, the controller in FIG.10B then determines at point 1010 that the first motion data of movementof the robot arm according to the third acceleration profile exceeds thefirst threshold motion metric. The controller then reselects the secondacceleration profile and instructs the motor to move the robot armaccording to the second acceleration profile. The movement of the robotarm according to the second acceleration profile results in a firstmotion data lower than the first threshold motion metric. Thus, thecontroller continues instructing the motor to move the robot armaccording to the second acceleration profile until the end effectorreaches the destination.

In FIG. 10B, there are two unused additional acceleration profiles.Movement of the robot arm according to any of the two additionalacceleration profiles is configured to result in a lower peak forceexerted on the semiconductor wafer than movement of the robot armaccording to the first acceleration profile. The controller in FIG. 10Bmay be configured to select one of the two additional accelerationprofiles if the first motion data of movement of the end effectoraccording to the first acceleration profile exceeds the first thresholdmotion metric.

FIG. 10C is a graph showing example partial acceleration profiles and anexample of the process of determining an operational accelerationprofile from a calibration acceleration profile.

In FIG. 10C, each example calibration acceleration profile has acorresponding example operational acceleration profile. The arrows showwhich example operational acceleration profile corresponds to whichexample calibration acceleration profile. The example calibrationacceleration profiles all have acceleration higher than theircorresponding example operational acceleration profile. Exampleoperational acceleration profiles accelerate at a lower rate than theircorresponding example calibration acceleration profiles to allow for asafety margin when semiconductor wafers are actually handled andtransported from station to station.

In the implementation in FIG. 10C, the controller first determines thecalibration acceleration profile. The controller determines thecalibration acceleration profile by determining which examplecalibration acceleration profile has a resulting first motion data lowerthan the first threshold motion metric as in blocks 702 to 708 of FIG.7. After the controller determines the calibration acceleration profile,the controller then selects the corresponding operational accelerationprofile as in block 710 of FIG. 7.

What is claimed is:
 1. An apparatus comprising: a first robot armconfigured to support a first semiconductor wafer on a first endeffector; a first optical sensor configured to detect relative movementbetween the first semiconductor wafer and the first end effector; and acontroller with one or more processors and a memory, wherein the one ormore processors, the memory, the first robotic arm, and the firstoptical sensor are communicatively connected and the memory storesprogram instructions for controlling the one or more processors to: a)cause the first robot arm to move according to a first accelerationprofile while the first semiconductor wafer is supported by the firstend effector, b) receive first optical sensor data from the firstoptical sensor, c) analyze at least the first optical sensor data todetermine first motion data based on relative movement of the firstsemiconductor wafer with respect to the first end effector during motionof the first robot arm while the first semiconductor wafer is supportedby the first end effector, d) determine whether the first motion dataattributable to movement of the first robot arm according to the firstacceleration profile exceeds a first threshold motion metric, and e)cause the first robot arm to move according to a second accelerationprofile when the first motion data attributable to movement of the firstrobot arm according to the first acceleration profile exceeds the firstthreshold motion metric, wherein the first motion data attributable tomovement of the first robot arm according to the second accelerationprofile stays within the first threshold motion metric.
 2. The apparatusof claim 1, wherein the first robot arm supports the first opticalsensor.
 3. The apparatus of claim 1, wherein the first optical sensor issupported in a location that is fixed with respect to the first robotarm.
 4. The apparatus of claim 1, wherein the first optical sensor isconfigured to interact with a pattern on the first semiconductor wafer.5. The apparatus of claim 1, further comprising a second sensorconfigured to detect relative movement between the first semiconductorwafer and the first end effector, wherein the memory further storesprogram instructions for controlling the one or more processors to:receive second sensor data from the second sensor, and analyze at leastthe first optical sensor data and the second sensor data to determinethe first motion data.
 6. The apparatus of claim 5, wherein the firstrobot arm supports the first optical sensor and the second sensor. 7.The apparatus of claim 5, wherein the second sensor is an opticalsensor.
 8. The apparatus of claim 7, wherein the second sensor isconfigured to interact with a pattern on the first semiconductor wafer.9. The apparatus of claim 5, wherein the first robot arm supports thefirst optical sensor and the second sensor is supported in a locationthat is fixed with respect to the first robot arm.
 10. The apparatus ofclaim 5, wherein the second sensor is selected from the group consistingof a machine vision sensor, a laser sensor, a dual laser sensor, a photobased sensor, a machine imaging sensor, a charge coupled device, abroken beam sensor, an accelerometer, ultrasonic sensor, and amechanical sensor.
 11. The apparatus of claim 1, wherein the firstoptical sensor is selected from the group consisting of a machine visionsensor, a laser sensor, a dual laser sensor, a photon based sensor, amachine imaging sensor, a charge coupled device, and a broken beamsensor.
 12. The apparatus of claim 1, wherein the first optical sensoris a laser sensor.
 13. The apparatus of claim 1, wherein the firstmotion data is based on data from which the relative angle of rotationof the first semiconductor wafer with respect to the first end effectorduring motion of the first robot arm while the first semiconductor waferis supported by the first end effector can be calculated.
 14. Theapparatus of claim 1, wherein the first motion data is based on acombination of two or more relative motion parameters selected from thegroup consisting of: relative acceleration of the first semiconductorwafer with respect to the first end effector during motion of the firstrobot arm while the first semiconductor wafer is supported by the firstend effector; relative velocity of the first semiconductor wafer withrespect to the first end effector during motion of the first robot armwhile the first semiconductor wafer is supported by the first endeffector; relative displacement of the first semiconductor wafer withrespect to the first end effector during motion of the first robot armwhile the first semiconductor wafer is supported by the first endeffector; and relative angle of rotation of the first semiconductorwafer with respect to the first end effector during motion of the firstrobot arm while the first semiconductor wafer is supported by the firstend effector can be calculated.
 15. A method comprising: a) moving afirst robot arm, including a first end effector supporting a firstsemiconductor wafer, according to a first calibration accelerationprofile; b) receiving first optical sensor data from a first opticalsensor configured to detect relative movement between the firstsemiconductor wafer and the first end effector; c) analyzing the firstoptical sensor data to determine first motion data based on relativemovement of the first semiconductor wafer with respect to the first endeffector during motion of the first robot arm while the firstsemiconductor wafer is supported by the first end effector; and d)determining whether the first motion data attributable to movement ofthe first robot arm according to the first calibration accelerationprofile exceeds a first threshold motion metric.
 16. The method of claim15, further comprising: e) determining that the first motion dataattributable to movement of the first robot arm according to the firstcalibration acceleration profile exceeds the first threshold motionmetric; f) moving the first robot arm, including the first end effectorsupporting the first semiconductor wafer, according to a secondcalibration acceleration profile; g) determining that the first motiondata attributable to movement of the first robot arm according to thesecond calibration acceleration profile does not exceed the firstthreshold motion metric; h) selecting a second operational accelerationprofile associated with the second calibration acceleration profile; i)moving the first robot arm, after h), according to the secondoperational acceleration profile associated with the second calibrationacceleration profile; j) determining, after i), whether the first motiondata attributable to the movement of the first robot arm according tothe second operational acceleration profile exceeds a second thresholdmotion metric; k) determining, after j), that the first motion dataattributable to the movement of the first robot arm according to thesecond operational acceleration profile exceeds the second thresholdmotion metric; l) selecting, after k), a third operational accelerationprofile; and m) moving, after l), the first robot arm according to thethird operational acceleration profile, wherein the first motion dataattributable to the movement of the first robot arm according to thethird operational acceleration profile stays within the second thresholdmotion metric; and n) determining, after m), that the first motion dataattributable to the movement of the first robot arm according to thethird operational acceleration profile does not exceed the secondthreshold motion metric.
 17. The method of claim 15, further comprising:e) determining that the first motion data attributable to movement ofthe first robot arm according to the first calibration accelerationprofile does not exceed the first threshold motion metric; f) selectinga first operational acceleration profile associated with the firstcalibration acceleration profile; g) moving the first robot arm, afterf), according to the first operational acceleration profile associatedwith the first calibration acceleration profile; h) determining, afterg), whether the first motion data attributable to the movement of thefirst robot arm according to the first operational acceleration profileexceeds a second threshold motion metric; i) determining, after h), thatthe first motion data attributable to the movement of the first robotarm according to the first operational acceleration profile exceeds thesecond threshold motion metric; j) selecting, after i), a thirdoperational acceleration profile; k) moving, after j), the first robotarm according to the third operational acceleration profile wherein thefirst motion data attributable to the movement of the first robot armaccording to the third operational acceleration profile stays within thesecond threshold motion metric; and l) determining, after k), that thefirst motion data attributable to the movement of the first robot armaccording to the third operational acceleration profile does not exceedthe second threshold motion metric.
 18. The method of claim 15, furthercomprising: e) determining that the first motion data attributable tomovement of the first robot arm according to the first calibrationacceleration profile does not exceed the first threshold motion metric;f) selecting a first operational acceleration profile associated withthe first calibration acceleration profile; and g) moving the firstrobot arm N additional times according to the first operationalacceleration profile for N additional semiconductor wafers when thefirst motion data attributable to the movement of the first robot armaccording to the first operational acceleration profile exceeds thefirst threshold motion metric and the first motion data attributable tothe movement of the first robot arm according to the first operationalacceleration profile does not exceed the first threshold motion metric,wherein N is an integer greater than or equal to
 1. 19. The method ofclaim 15, further comprising: e) determining that the first motion dataattributable to movement of the first robot arm according to the firstcalibration acceleration profile does not exceed the first thresholdmotion metric; f) selecting a third calibration acceleration profile; g)moving, after f), the first robot arm according to the third calibrationacceleration profile; h) determining, after g), that the first motiondata attributable to movement of the first robot arm according to thethird calibration acceleration profile does not exceed the firstthreshold motion metric; i) selecting, after h), a third operationalacceleration profile associated with the third calibration accelerationprofile; j) moving, after i), the first robotic arm according to thethird operational acceleration profile associated with the thirdcalibration acceleration profile; and k) determining, after j), that thefirst motion data attributable to movement of the first robot armaccording to the third operational acceleration profile does not exceedthe first threshold motion metric.
 20. The method of claim 15, whereinthe first optical sensor is selected from the group consisting of amachine vision sensor, a laser sensor, a dual laser sensor, a photonbased sensor, a machine imaging sensor, a charge coupled device, and abroken beam sensor.